Transformer protection.



No. 788,583. PATENTED FEB. 28, 1905. W. S. MOODY.

TRANSFORMER PROTECTION.

APPLICATION FILED JULY 25, 1904.

\AHTNEI55E5 INVENTOR UNITED STATES Patented February 28, 1905.

PATENT OEEIcE.

WALTER S. MOODY, OE SCHENECTADY, NEIV YORK, ASSIGNOR TO GEN- ERALELECTRIC COMPANY, A CORPORATION OF NEW YORK.

TRANSFORMER PROTECTION.

SPECIFICATION forming part of Letters Patent No. 783,533, dated February28, 1905.

Application filed July 25, 1904. Serial No. 218.032.

To all whom, it may concern.-

Be it known that I, WALTER S. MOODY, a citizen of the United States,residing at Schenectady, county of Schenectady, State of New I York,have invented certain new and useful Improvements in TransformerProtection, of which the following is a specification.

This invention relates to systems of electrical distribution in whichcurrent at high potential is distributed to points near the place ofconsumption and there tlitIlSfOl'Il'lBd or converted into current ofsuitable working pressure. In transformers used in such systems theprimary or high-pressure circuit and the secondary or low-pressurecircuit are normally insulated from each other; but if by any accidentthe insulation should fail the secondary circuit, together with all theinstruments or power apparatus connected to it, would be raised to thepotential of one side of the primary circuit. Under these conditions adischarge might occur through ground to the other side of the primary,thus endangering life and property along the secondary circuit.

It is old in the art to protect the secondary circuit from the highvoltage of the primary by providingapermanent connection between thesecondary and ground. This arrangement is sometimes insufficient toprotect the secondary circuit, for the reason that the currentdischarged through the secondary and the ground connection is sometimessufficient to fuse the part of the secondary traversed by the dischargeand to burn off the connection with the ground-wire. This leaves theremainder of the secondary winding and the entire secondary network atthe dangerously high potential of the primary circuit. In the presentinvention this difficulty is overcome by connecting the secondary to thecore of the transformer or converter and grounding the core through aheavy connection in a manner hereinafter described.

While the invention is readily applicable to various forms of electricalapparatus, it is particularly useful in connection with transformers ofthe type commonly designated as current-transformers and usedinconnection with central-station instruments.

The accompanying figure shows diagrammatically the application of theinvention to such a device.

1 indicates the source of power, and 2 3 the high-potentialdistributing-mains. The annular iron cor-e4 represents the core of thecurrent-transformer, having a primary 5, consisting of a straightcylindrical conductor, carrying the high-potential current of the-line,and a winding 6, connected to the switchboard instrument 7. The winding6 is insulated from the iron core 4 throughout its length, except at 8,whereit is permanently grounded to the core. In the finished transformerthis grounded point is preferably about midway between the two ends ofthe secondary coil. The insulation 10 between the core and the secondarywinding is comparatively thin and is weak enough to be punctured if subjected to the voltage of the primary circuit. The iron core 4: ispermanently connected to earth by a conductor 9, capable of carrying thefull primary current. The transformer may be provided with a metal case11, surrounding the windings. Bushings 12, 13, and 14: serve to insulatethe case from the winding-terminals, and a conductor 15, capable ofcarrying the full primary current, connects the case with theground-conductor 9.

IVith the arrangement described if the secondary winding is subjected tothe dangerous voltage of the primary circuit because of the failure ofthe insulation or similar cause the high-pressure current will escapethrough the connection 8 to the ground-conductor 9 and then to earth. Ifthis leakage-current is of sufficient magnitude to fuse the grounded endof the secondary winding, the escape of the high-voltage current toground will not be prevented thereby, but will take place through thethin core insulation, .and thus from the core to ground, as before.

The excessive heating of the secondary materially assists in breakingdown this thin core insulation, and so long as any of thesecondarywinding remains intact there will be a low-resistance path to earth forthe highvoltage current.

I f the primary becomes grounded to the case in any manner, as byfailure of the bushing 13, the high-potential current will be carried toearth by the heavy conductors 15 and 9, thus preventing a possiblebreakdown of the secondary bushings and the destruction of the secondaryterminals by the high-potential current.

WV hat I claim as new, and desire to secure by Letters Patent of theUnited States, is

1. In a transformer, a core, a winding therefor, an electricalconnection between the core and winding, and means for connecting thecore to earth.

2. In a transformer, a core, a winding therefor, and an electricalconnection between said winding and core.

3. A transformer comprising a case, acore, a high-potential winding, alow-potential winding, an electrical connection between saidlow-potential winding and core, and means for connecting said case andcore to earth.

L A transformer comprising a core, a lowpotential winding, thininsulation between said winding and core, an electrical connectionbetween the core and winding near the center of the winding, and meansfor connecting the core to earth. i

5. A transformer comprising a core, a winding therefor, thin insulationbetween said winding and core, an electrical connection be tween saidcore and winding, and means for connecting the core to earth.

6. A transformer comprising a core, a winding therefor, an electricalconnection between said core and winding near the center of said.winding, and means for connecting the core to earth.

7. A transformer comprising a case, a core, a winding for said core, anelectrical connection between said core and winding near the center ofsaid winding and means for connecting the caseand core to earth.

8. A transformer comprising a case, a core, a low-potential winding forsaid core, thin insulation between said winding and core, an electricalconnection between the core and Winding near the center of the winding,and means for connecting the case and core to earth.

In witness whereof I have hereunto set my hand this 21st day of July,1904.

WALTER S. MOODY.

\Vitnesses:

BENJAMIN B. HULL, HELEN URFORD.

